There are provided particular porous materials. LIQUID CRYSTALS, AMPHIPHILES, MICELLES, LYOTROPIC PHASES
Amphiphilic compounds, also referred to as amphiphiles, surface-active agents or surfactants, are composed of molecules to which contain both at least one polar or hydrophilic "head" group and at least one non-polar or hydrophobic "tail". In aqueous solution, amphiphilic compounds may associate with each other to form structures known as micelles. These micelles are most often spherical structures in which the polar head groups form the outer surface and the non-polar tails form the inner portion or core of the sphere. Micelles are stable colloidal aggregates which are formed by amphiphiles above a specific concentration, which is called the critical micelle concentration or "CMC". Amphiphiles often have the further ability to arrange into various other, energetically favorable, ordered structures (e.g, liquid crystalline phases) in solution in response to certain stimuli. These stimuli include concentration of the amphiphile, temperature, pressure, ionic composition of solution, presence of organic or inorganic species in solution, etc.
The head group of an amphiphile may bear a positive or negative charge. Anionic amphiphilic compounds have a hydrophilic head group which bears a negative charge; a typical anionic amphiphilic compound is R--O--SO.sub.3 --, in which R represents a hydrocarbon chain, the hydrophobic "tail" group. The negative charge associated with the anionic head group is usually balanced by a small cation, such as H+, Na+, K+ or NH.sub.4 +. Cationic amphiphilic compounds have a hydrophilic head group which bears a positive charge; a typical cationic amphiphilic compound is R(CH.sub.3).sub.3 N+ where R again represents a hydrocarbon chain (the tail group). The positive charge associated with the cationic head group is usually balanced by a small anion, such as OH--, Cl--, Br-- or SO.sub.4 .dbd.. The length of the chain (R) is critical to the function of an amphiphilic species, as, in aqueous solution, hydrocarbon chain lengths below 6 carbons do not energetically favor aggregation to form micellar phases, and carbon chain lengths above 36 carbons do not exhibit sufficient solubility to achieve CMC status. There exist other amphiphilic compounds, some bearing no net charge, that produce liquid crystal phases in solution. These include the general classes of nonionic and zwitterionic surfactants. An exhaustive review of this chemistry is found in a review article by Winsor, Chemical Reviews, 68, 1, (1968).
Liquid crystals are materials which exhibit aspects of both the crystalline solid and amorphous liquid state. They resemble liquids in their ability to flow, and solids in the degree of order within their structure. In many systems this order is established spontaneously. In other cases, it can be brought about, or controlled, by electric, magnetic, or hydrodynamic fields. Lyotropic liquid crystals comprise a large body of known liquid crystalline systems. These lyotropic systems are often comprised of two components: a solvent (e.g, water) and an amphiphilic compound. In many cases, however, additional components such as salts or other inorganic or organic compounds may be present in a lyotropic system. Such solvent-containing systems are often referred to as solutions, although it will be understood that such solutions are not true molecular solutions insofar as amphiphilic compounds are present as micellar aggregates as opposed to individual molecular species.